At least 19 of the passengers were also injured, including six seriously, the official added.
The bus had around 60 people on board when it crashed on a main highway south of the small town Sveg.
The bus reportedly was en route to a ski resort on Sunday morning, according to local media.
Pictures showed the bus lying on its side in a ditch beside the highway approximately 260 miles northwest from the capital, Stockholm.
The cause of the accident is not yet known but the road reportedly was icy when the accident occurred at about 7 am (0600 BST).
No further details were immediately available.
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